Guerilla natural farming over tall grass.

What seeds are likely to fare well in the battle against tall perennial grass?

Broad casting of what will help to shade the grass out or out stretch it in hight? Ideally an annual crop.

I live in Kansas, where grass is one tough customer! Depending on the variety of grass, it really will grow "as tall as the withers on a horse", as the saying went.

The think is, wheat is also grass, and it also does well here.

From what I have seen and done in my own back yard, you might try mowing the grass in the Fall and then planting winter wheat in the now-short grass. When I speak of planting, I mean to broadcast the seed over the top of the mown grass just before a rain. I have some volunteer wheat in my lawn, and I sprinkled some seed on the lawn in the spring. The volunteer wheat from last Fall did the best by far.

I am leaving some of it for another month, at which time it should be ripe. I can get seed off of it and re-sow it in a less VISIBLE area!!!

If you have enough water to support it's growth, a vigorous annual vine such as winter squash, pumpkin, bottle gourds, sweet potato, vining cowpeas, and such like would be a possibility. You need to make some enriched holes in the grass to plant these in, and then make a little circle of sheet-mulch about 3-4 feet across around each. Once the vines are long enough to start running up into the grass they will weigh it down flat and start to smother it.
In a small area, I've sheetmulched tall grass, shoulder-high brambles, and such like by first rolling them down flat with a barrel, and then proceeding with cardboard.....

In most case established undisturbed grassland will not have many vacant niches. Forest will replace grass eventually in many temperate areas by succession. In some parts of the world grassland is the climax vegetation.

In my experience, seedballing anything into established, undisturbed grass will achieve nothing whatsoever. Very occasionally something will find enough bare soil and light to grow, but it is very unlikely to outcompete the tough wild grasses which will have been slugging it out with each other for years.

Cut the grass close to the ground for compost/hay, then either smother it with cardboard,carpet or plastic, solarise it (if you have enough sun), make compost heaps on top of it (and turn them and move them every two months) or turn pigs or chickens into it and you will be able to make a start growing whatever you want to grow.